Low Permeability Clayey Soil Research Articles

Enhancing biocementation performance in low permeability clayey soil through sand column strategy

Soil erosion is a common phenomenon which causes lots of geological and engineering disasters. Clayey soil erosion control is a hot research topic and a challenging issue for its low permeability and lack of effective infiltration of treatment solutions. In this study, a coupling microbially induced calcium carbonate precipitation (MICP)-sand column method was proposed as a promising and sustainable technique to mitigate surface clayey soil erosion with adjustable treatment depth. Seven groups of soil samples were prepared, including pure soil, MICP-treated soil, and MICP-sand column method-treated soil. A series of disintegration tests and penetration tests were conducted to investigate the method feasibility and adjusting mechanism of erosion mitigation with varying sand column heights and diameters. Compared to pure soil sample, sample treated by MICP-sand column (6 cm-height and 3 cm-diameter) method could reach a maximum reduction of 50 % in ultimate disintegration rate and a 30 % increase in the highest penetration resistance. The sample has a 7.9 cm effective treatment depth, which is 5.3 times of the MICP-treated sample. The mechanism of erosion mitigation can be attributed to that the sand column serves as a favorable path for the bacteria suspension and cementation solution in low-permeability-clayey soil and improves the effective depth of MICP treatment. Adjusting the height and diameter of sand column can change the calcium carbonate distribution, especially at the locations near the surface and around the sand column. In this study, the optimal height and diameter are 6 cm and 3 cm, respectively, and finally form a U-shape three-layer structure. The structure significantly increases the proportion of the hard crust layer and weak-cemented layer with high hydro-mechanical properties. In conclusion, the coupling MICP-sand column method with reasonable height and diameter of sand column shows the ability to control surface erosion of soil and has better long-term mitigation performance.

Approximate analytical solution to the axisymmetric model for PVD-enhanced in-situ flushing of double-layered contaminated soils

The in-situ soil flushing technique which utilizes prefabricated vertical drains (PVDs) is an effective remediation method for sandy, silt, and low-permeability clayey soils. It offers several advantages, such as reducing the seepage path, achieving uniform flushing of contaminated areas, and shortening the construction time. This paper proposes an axisymmetric analytical model for PVD-enhanced in-situ flushing remediation of double-layered contaminated soils considering the decay of the initial contaminant concentration along the depth. The derived solutions are then verified against experimental results and existing analytical solutions. The accuracy of the simplified solution is found to improve as the number of stratifications increases by vertically dispersing the initial contaminant concentration, as compared to the numerical results obtained from COMSOL Multiphysics. The study also reveals that a decrease in the spacing between adjacent injection and extraction PVDs or an increase in the injection/extraction rate enhances the flushing efficiency. However, the effects of the two parameters on soil remediation are non-linear and linear, respectively. Furthermore, the difference in the geotechnical properties of the upper soil layers in a bi-layered contaminated soil leads to a variation in the contaminant concentration at any depth and this variation grows larger with time until the soil is completely remediated.

Simulating 3-D water flow in subsurface drain trenches and surrounding soils in a clayey field

Subsurface drain trenches are important pathways for water movement from the field surface to subsurface drains in low permeability clayey soils. The hydrological effects of trenches installed with well conducting backfill material and gravel inlet patches are difficult to study with only experimental methods. Computational three-dimensional soil water models provide additional tools to assess spatial processes of such drainage system. The objective was to simulate water flow pathways with 3-D FLUSH model in drain spacing and trench depth scale with two model configurations: (1) the total pore space of soil was treated as a single continuous pore system and (2) the total pore space was divided into mobile soil matrix and macropore systems. Both model configurations were parameterized almost solely with field data without calibration. Data on soil hydraulic properties and drain discharge measurements were available from a clayey subsurface drained agricultural field in southern Finland. The effect of soil hydraulic variability on water flow pathways was assessed by generating computational grids in which the hydraulic properties were sampled randomly from five measured soil sets. Both model configurations were suitable to describe the recorded drain discharge, when model was parameterized in finer scale than drain spacing and the parameterization described highly conductive subdomains such as macropores in a dual-permeability model or the trench in a single pore system model. Models produced similar hourly discharge and water balance results with randomly sampled soil hydraulic properties. The results provide a new view on consequences of soil heterogeneity on subsurface drainage. The practical implication of the results from different drainage scenarios is that gravel trench appears to be important only in soils with a poorly conductive subsoil layers without direct macropore connections to subsurface drains. Solely drain discharge data was not sufficient to determine the differences in water flow pathways between the two model configurations and more output variables, such as groundwater level, should be taken into account in making assessments on the effects of different drainage practices on field drainage capacity.

Electrokinetic Delivery and Activation of Persulfate for Oxidation of PCBs in Clayey Soils

Contamination of soils by polychlorobiphenyls (PCBs) is of environmental concern because of their toxicity, persistence, hydro- phobic nature, and slow biodegradation potential. Among the PCB remedial technologies, direct oxidation by persulfate is considered to have great potential to be both simple and rapid. However, to produce faster reaction rates, persulfate is often activated using heat, metal chelates, hydrogen peroxide, or high pH. Furthermore, delivery of persulfate in low permeability clayey soils is difficult. Integrating electrokinetic re- mediation with persulfate has the potential to overcome such difficulties because the applied electric potential can facilitate the delivery of per- sulfate in low permeability soils as well as activate oxidizing radicals and simultaneously induce oxidative/reductive reactions directly in the soil.ThisstudyinvestigatesthepotentialforinsituoxidationofPCBsinlowpermeabilitysoilsusingpersulfateasanoxidantandalsoevaluates the benefits of integrating oxidation with electrokinetic remediation. Several series of laboratory batch and bench-scale electrokinetic experi- ments were conducted using kaolin, a representative clayey soil, spiked with 50 mg/kg of 2,2 0 ,3,5 0 tetrachlorobiphenyl (PCB 44), a represen- tative PCB. Persulfate oxidation activators (elevated temperature (45� C) and high pH (at the cathode)) were investigated to maximize the PCB degradation. In addition, the effect of oxidant dosage on PCB degradation was investigated. The electrokinetically enhanced temperature-only activated persulfate oxidation test resulted in better PCB 44 remediation (77.9%) than the temperature and high-pH activated persulfate oxidation(76.2%)ina7-dayperiod.Theoptimaldosageforeffectiveremediationwas30%Na-persulfate(76.2%)becausea20%concentration of the oxidant yielded a lower rate of degradation (55.2%) of PCB 44. The results are encouraging for the use of electrokinetically enhanced persulfate oxidation for the effective remediation of PCBs in soils.DOI:10.1061/(ASCE)GT.1943-5606.0000744. © 2013 American Society of Civil Engineers. CE Database subject headings: Remediation; Soil treatment; Oxidation; Clays; PCB. Author keywords: Electrokinetic remediation; Soil remediation; Persulfate oxidation; Advanced oxidation process; Polychlorobiphenyls.

Combined use of a transformed red mud reactive barrier and electrokinetics for remediation of Cr/As contaminated soil

A reactive barrier (RB) of transformed red mud (TRM), a by-product of the refinement of bauxite in alumina production, was placed adjacent to the anode of an electrokinetic (EK) system with the aim of enhancing removal of chromium or arsenic, added singly to a low permeability clayey soil, and favouring entrapment. The innovative study focused on evaluation of the synergic interaction between the EK system and the RB, and of the efficiency when compared to traditional EK remediation (control tests). The results obtained underlined the successful outcome of treatment of the Cr(VI)-contaminated soil. In presence of the TRM RB, 19.4% wt. of total Cr content was detected in the anolyte and 20.6% wt. trapped in the anodic RB after 6 d, versus 6.6% wt. in the anolyte and 8.8% wt. in the soil adjacent to the anode following the control run without RB. On increasing duration of treatment up to 12 d, 60.8% wt. of total initial Cr was found in the anolyte and 25.5% wt. trapped in the RB, versus 9.1% wt. and 5.3% wt., respectively, after a control run of the same duration. Finally, on increasing the mass of TRM in the RB, 60.6% wt. of initial Cr content was found to have accumulated in the RB, with Cr being completely absent from the anodic chamber. Conversely, combined treatment was much less effective on As contaminated soil, at least under the operative conditions applied. Low initial As concentration and interference with iron oxides in the soil were likely the reasons underlying low efficiency while attempting As decontamination.

Electrokinetic-enhanced transport of lactate-modified nanoscale iron particles for degradation of dinitrotoluene in clayey soils

This study investigated the transport and reactivity of bare nanoscale iron particles (NIP) and lactate modified NIP (LM-NIP) in low permeability clayey soils contaminated with dinitrotoluene (DNT) under applied electric potential. Bench-scale electrokinetic experiments were performed at constant voltage gradient (1 VDC/cm) with DNT spiked kaolinite at a concentration of 920 mg/kg. A cylindrical Plexiglas cell (3.81 cm inner diameter, 13.5 cm length) specially designed for this study was used. NIP or LM-NIP at a concentration of 4 g/L was injected at location 3 cm from the anode. Aluminum lactate 10% (w/w) was used as modifier for LM-NIP. The results showed 41–65% of DNT degradation in the soil near the anode, while it was lower at 30–34% near the cathode. The highest DNT degradation was achieved using LM-NIP. The total degradation of DNT was attributed to both NIP and electrochemical process. Overall it was found that electrokinetic system can enhance the delivery of nanoscale iron particles in low permeability soils for the degradation of energetic organic contaminants such as DNT.

Reactivity of Aluminum Lactate-Modified Nanoscale Iron Particles with Pentachlorophenol in Soils

Abstract Due to the hindered transport of nanoscale iron particles (NIP) in the subsurface caused by the agglomeration and adsorption of NIP during transport, the NIP surface has to be modified to improve the transport of NIP in the subsurface. This study assessed the effectiveness of surface-modified NIP for in situ degradation of contaminants using aluminum lactate as the modifying agent, where aluminum lactate had been earlier shown to be an effective dispersant for enhanced transport of modified NIP in the subsurface. The reactivity of bare-NIP and lactate-modified NIP (LM-NIP) was investigated using pentachlorophenol (PCP) as a representative chlorinated hydrophobic organic contaminant in kaolin and field sand as low permeability clayey soil and high permeability soil, respectively. Kaolin and field sand were spiked at 100 mg/kg PCP and at 89 mg/kg PCP, respectively. NIP dosages of 4, 10, 20, 50, 75, and 100 g/L were applied for a reaction period of 24 h. For the bare-NIP dosage of 100 g/L, PCP degra...

Fenton-Like Oxidation of Polycyclic Aromatic Hydrocarbons in Soils Using Electrokinetics

An integrated electrochemical oxidation process that utilizes electrokinetics (EK) to deliver the oxidant (5–10% hydrogen peroxide, H2 O2 ) and chelant [40 mM of ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA)] or iron chelate (1.4 mM Fe-EDTA or Fe-DTPA) to oxidize polycyclic aromatic hydrocarbons (PAHs) in soils was investigated. Batch and bench-scale EK experiments were conducted using: (a) kaolin, a low permeability clayey soil, spiked with phenanthrene at 500 mg/kg, and (b) former manufactured gas plant (MGP) soil, a high buffering silty soil, contaminated by a variety of PAHs (1493 mg/kg). Batch experiments showed that chelant solutions dissolve native iron minerals to form soluble Fe-chelates that remain available even at higher pH conditions of soil for the Fenton-like oxidation of the PAHs. In EK experiments, a 5–10% H2 O2 solution was delivered from the anode and a chelant solution or iron-chelate was delivered from the cathode. Preflushing of soil with 5% etha...

Sequential Electrokinetic Remediation of Mixed Contaminants in Low Permeability Soils

The coexistence of heavy metals and polycyclic aromatic hydrocarbons (PAHs) at many of the contaminated sites poses a severe threat to public health and the environment. Very few technologies, such as soil washing/flushing and stabilization/solidification, are available to remediate such sites; however, these technologies are ineffective and expensive to treat contaminants in low permeability clayey soils. Previous studies have shown that electrokinetic remediation has potential to remove heavy metals and organic compounds when they exist individually in clayey soils. In the present study, the feasibility of using surfactants and organic acids sequentially and vice versa during electrokinetic remediation was evaluated for the removal of both heavy metals and PAHs from clayey soils. Kaolin was selected as a model clayey soil and it was spiked with phenanthrene and nickel at concentrations of 500 mg/kg dry each to simulate typical field mixed contamination. Bench-scale electrokinetic experiments were perfor...

Removal of Nickel and Phenanthrene from Kaolin Soil Using Different Extractants

Numerous sites exist where low permeability clayey soils have been contaminated with both polycyclic aromatic hydrocarbons (PAHs) and heavy metals. To remediate these sites, innovative treatment methods are urgently required. Electrokinetically enhanced in situ flushing offers great potential to remediate low permeability soils, but this method is highly dependent on the type of extracting solution used. This study investigated the feasibility of using different extracting solutions at various concentrations to remove PAHs as well as heavy metals from low permeability clayey soils. The most efficient extracting solutions could be used as purging/extracting solutions in electrokinetic remediation and other technologies such as soil washing. For the present study, kaolin was selected as a model clayey soil, and it was spiked with phenanthrene as well as nickel at concentrations of 500 mg/kg each to simulate typical field contamination. Several batch tests were conducted using a known amount of the spiked ka...

Nutrient Amendment for the Bioremediation of a Chromium-Contaminated Soil by Electrokinetics

This article presents the results of a preliminary laboratory investigation wherein electrokinetics was used for the delivery of nutrients to metal-reducing micro-organisms in a low permeability clayey soil. In particular, the micro-organisms were used to reduce a toxic and mobile heavy metal (hexavalent chromium or Cr(VI)) to a less toxic and immobile form (trivalent chromium or Cr(III)). Three bench-scale electrokinetic experiments were conducted using kaolin as a model low permeability clayey soil, and the kaolin was artificially contaminated with Cr(VI) at an initial target concentration of 1,000 mg/kg. All the experiments were conducted with a constant electrical voltage gradient of 1.0 V/cm and included a control test without micro-organisms or nutrients, a test with micro-organisms but without nutrients, and a test with micro-organisms and supplemental nutrients, specifically acetate, phosphate, and ammonium. The results showed that acetate and phosphate amendment by electrokinetics was effective because both nutrients electromigrated into the soil. Moreover, the results indicate that employing the micro-organism cultures improved Cr(VI) reduction. These results suggest that nutrient amendment by electrokinetics for the bioremediation of heavy metals has great potential; however, the microbial strains responsible for Cr(VI) reduction must be identified so the electrokinetic system can be engineered to provide the optimal nutrient, pH, and environmental conditions for these strains.

Effects of system variables on surfactant enhanced electrokinetic removal of polycyclic aromatic hydrocarbons from clayey soils

Numerous polycyclic aromatic hydrocarbon (PAH)‐contaminated sites threaten public health and the environment because PAHs are commonly toxins, mutagens, and/or carcinogens. PAHs are hydrophobic and resistant to degradation; therefore, conventional remediation methods are often costly or inefficient, especially when the PAHs are present in low permeability clayey soils. Electrokinetically enhanced in‐situ soil flushing is an innovative technology that has the potential to greatly increase soil‐solution‐contaminant interaction and remedial efficiency, even under low permeability soil conditions. Although this technique is promising, many system variables may affect remedial efficiency, such as the surfactant concentration, pH control, and voltage gradient. The objective of this investigation was to evaluate the effects of these system variables. Bench‐scale electrokinetic experiments were conducted using various operating conditions, which included deionized water or a 3% or a 5% surfactant concentration flushing solution. Additional tests were also conducted using the 5% surfactant concentration along with a higher pH solution or a larger voltage gradient. The experiments employing the surfactant flushing solution had a lower electroosmotic flow but exhibited greater contaminant desorption, solubilization and migration. The benefits of using a higher pH solution or a larger voltage gradient were difficult to discern because changing these process variables did not significantly improve remedial efficiency. Overall, the results indicated that the surfactant flushing solution was advantageous for treating the soil near the anode region, but contaminant migration was limited by changes in the soil and/or solution chemistry that occurred with time and/or distance from the anode

A Method for Predicting Chloride Concentrations in Leachate at Natural Attenuation Landfills in the Precambrian Shield Regions of Ontario, Canada

Natural attenuation landfill sites continue to be the preferred method of domestic waste disposal in the Precambrian Shield regions of Ontario due to economic factors. The main challenge in siting these landfills is ensuring that there will be no adverse impact on off-site water resources. Impact risk assessments are generally based on estimated volumes and strengths of chloride in the leachate. While volumes can be estimated using simple water balances, peak chloride concentration predictions are based on judgment and are quite variable. Since design chloride strengths dictate the size of the required attenuation zone, overestimating concentrations will typically make it impossible to find a suitable site, while underestimating concentrations increases the potential for adverse off-site impacts occurring. Hydrogeological data from active and closed landfills in the Precambrian Shield region were collected to help develop a reliable method of predicting peak chloride concentrations in leachate. This study focused on 21 sites located on relatively permeable sandy soils since landfills underlain by low permeability clayey soils retain leachate similar to lined facilities. Linear regression analyses were conducted to determine if source chloride concentrations at the “sand” sites are significantly influenced by waste thickness, fill area, waste volume, waste deposition rate, hydraulic conductivity, upgradient flow length, depth to the water table, and moisture surplus. A strong relationship (R = 0.957) was found to exist between source chloride concentrations and waste volume. This empirical volume versus chloride regression equation can be used as the basis for establishing design chloride concentrations at new natural attenuation landfills developed over sandy soils in the Precambrian Shield regions of Ontario. An alternative risk assessment approach is required for sites developed over clay soils.